1. Field of the Invention
This invention relates to stainless steels of high chromium content and particularly to stainless steels having as low a carbon content as possible. This invention is concerned with stainless steels having excellent corrosion resistance and resistance to intercrystalline corrosion. More especially, this invention relates to an improved process for producing such steels wherein the amount of inert gas normally required during a first refining phase can be reduced without significant increase in the amount of time required for the refining operation.
2. Discussion of the Prior Art
A process for producing such stainless steels is known from the German Offenlegungsschrift No. 25 25 355, wherein a steel melt containing chromium or chromium and nickel with higher carbon contents, e.g., 1%, is refined in a converter which has at least one blast nozzle below the bath level and at least one blast lance above the bath level, whereby in several refining phases oxygen is supplied to the steel melt through the blast lance and inert gas through the blast nozzle in the first refining phase and in the succeeding refining phases oxygen combined with inert gas is supplied to the steel melt through the blast nozzles. It is here recommended to reduce the proportion of oxygen supplied in relation to the proportion of inert gas with a decreasing carbon content in the steel melt. A corresponding step is described, for example, in the publication "Stahl und Eisen" 1976, on pages 1255/1256.
In carrying out such a process the blast lances are no longer used in the succeeding refining phases following the first refining phase, the refining means being introduced exclusively by being blown through the nozzles. Generally speaking, the refining means (oxygen) is combined with an inert gas, in particular argon. In order to carry out the refining process in an economically feasible manner and within a reasonable time, it is desirable to supply as much gas as possible to the steel melt in the succeeding refining phases. As this can only occur through the nozzles, it has heretofore been necessary to employ blast nozzles with a correspondingly large cross-section. This has meant that a high amount of inert gas has been employed in the first refining phase--an amount of inert gas substantially greater than would be required by the demands of the first refining phase. The first refining phase requires only that amount of inert gas introduced through the nozzles to circulate the molten steel and to cool the nozzle itself. At the same time, the blowing in of inert gas prevents the molten steel from penetrating into the blast nozzles. As stated heretofore, a large amount of inert gas was necessary to protect the blast nozzles.
It is an object of this invention, therefore, to provide a process which enables a decrease in the proportion of inert gas introduced into the first refining phase while maintaining a short refining period.